Fusion of eutectic compositions is a well-known phenomenon. Fusion essentially means melting, and eutectic fusion describes the phenomenon of a combination of two materials at a generally closely defined temperature which is well below the melting point of either of those materials itself. Thus, the melting point of the first material lowers as some quantity of the second material is added to it, until a certain temperature called the eutectic melting point, which is the lowest melting point for the particular composition. Thereafter, as the ratio of the two elements is increased in the favour of the second element, the melting point again begins to arise. The composition at which the lowest melting point occurs is the eutectic composition, and is expressed in terms of percentages of the two elements or materials being alloyed.
A typical, and very well known, eutectic composition is one which the present invention particularly utilizes in a principal application of the invention. That is the eutectic composition of tin and lead, which occurs when there is a mixture of 37% of lead with 63% of tin. Its eutectic melting point is 361.degree. F.
A number of other elements and materials exist, however, for which eutectic compositions can be made of those materials together with suitable alloying agents. They include numerous ferrous materials such as nickel vanadium steel, refractories, certain ceramics, and so on.
Because the eutectic melting point of a eutectic composition of a material together with its alloying agent occurs at a temperature below the melting point of either the material or the alloying agent itself, as a composition comprising a material together with an alloying agent increases in temperature, it will first reach the eutectic melting point for that combination of materials and the mixture becomes molten. When the mixture becomes molten, it becomes wet, so that a certain amount of flow of the molten eutectic composition can be expected to occur. It is these features of which the present invention is particularly cognizant, and the application of those features in a quite unexpected manner results in the production of solid compositions which are primarily of a first material or element, together with a small portion of another material or element which is an alloying agent for the first material under the correct--and controllable--conditions.
The present invention is particularly directed to materials which are, in general, unsinterable, and where a sintered and solid element of that material is desired to be produced. Solid elements made of a sintered material are generally quite frangible, and may have a very high porosity and high effective surface area. This may be particularly useful in such purposes and conditions as negative plates for lead acid batteries. The negative plate of a lead acid battery has, as its active component, elemental lead; the positive plate, of course, has lead oxide as its active component, where the electric couple between the plates is effected in the presence of an acidic electrolyte.
Other purposes to which the present invention may be directed include any kind of situation where a eutectic composition can be made of a material together with an alloying agent, where the liquid and therefore wet eutectic mixture at the eutectic melting point can be utilized in such a manner that adjacent wetted or melted areas may be joined together. Due to the nature of eutectic compositions, if the temperature of the wetted and melted areas of the eutectic composition is maintained at a temperature just above the eutectic melting point, then diffusion of the alloying agent into the material will continue, so that the ratio of the alloying agent and the material changes with the amount of the alloying agent remaining in the melted area becoming less. This drives up the melting point of that ratio of the composition, and the composition begins to "freeze" or "resolidify" because it is now below its melting point. Of course, it is recognized that the words "freeze" and resolidify, in the present context, applies to a composition that may be at a relatively high elevated temperature compared with, say, room temperature.
In any event, utilizing the phenomenon discussed above provides a means whereby surface treating and welding or surface joining (also identified as soldering in certain circumstances) may be achieved.
Thus, the present invention will provide sintered and solid elements which might be essentially self standing, although frangible. More usually, however, the present invention is utilized to provide a sintered and solid element which may otherwise secured to a supporting structure of some sort. Indeed, the present invention can be utilized in such a manner that a sintered and solid element can be formed in a bounded volume so as to join two other surfaces that protrude into that bounded volume, together. A typical example may be bonding two facing surfaces together, or two facing ends of wire together, using a suitable volume bounding agent in the sense of a tinker's dam.
Indeed, in some respects it is convenient to consider the alloying agent for the otherwise unsinterable material somewhat in the context of that as a dopant. However, the alloying agent may serve the purpose of a dopant in the sense of a modifier by which the functioning characteristics of a material such as dendrite suppression that has been doped are changed; but it does serve the purpose of being a melting point modifier, by which the melting point of the wetted and melted areas will be changed. Thus, the production of a solid and sintered element from an otherwise unsinterable material is effected by following the present invention. Refractory materials, such as those used as the target electrode in an X-Ray tube may thus be produced; it being noted that those refractory materials are not otherwise sinterable, and that the presence of a small quantity of the alloying agent would not harm and might enhance the X-Ray tube operation.